Whereas it has always been important to design a fluid flow system to accommodate the maximum demand. This has been fairly regularly accomplished when a stable demand has been predicted. In the past raw sewage has been combined with natural drainage and the drainage system has included drain pipes larger than the predicted normal flow to accommodate all flows at all times so it would not back up under times of unexpected demand. With the increased interest and concern for the environment and health of our expanding population it is important to channel raw sewage into one sewer system for proper treatment prior to discharge and the natural drainage or storm sewage and ground water into another system, which, because of its lack of contaminants may be discharged with little or no preliminary treatment. For reasons of efficiency, as well as best usage of treatment facilities, it is imperative that the system for handling raw sewage handle nothing more than raw sewage. The raw sewage will be fed into raw sewage treatment plants without overloading the facility and the environmental danger eliminated. It is for this reason that those systems which handle raw sewage must be monitored to predict any unpredicted increase in demand due to storm inflow or ground water infiltration. The monitoring of the flow further enables an observer to quickly recognize an increase and/or decrease caused by a failure of the sewage system which admits ground water infiltration or surface drainage into the system or alternatively releases raw sewage to the surrounding environment.
With the need for a monitoring program employing portable, continuously recording equipment in mind it has been suggested, and in many cases actively pursued, that the fluid flow within existing raw sewage systems be monitored either on a continual basis or intermittently over a period of time such that infiltration, inflow and the increase and/or decrease in demand be readily predicted and accommodated.
A means for determining the flow within an open conduit is through the use of the Manning flow relationship wherein if the pipe size is known, the slope of the pipe or conduit, and the material of the conduit as well as the recorded depth, then using the Manning formula the flow can be determined. One method of recording the depth in the past has been through the use of a "Manning dipper" which essentially is a plumb bob lowered through a manhole entry to the sewer liquid flow surface. It would record the depth of the liquid in the manhole and thus the flow could be approximately be determined. One of the disadvantages of the Manning dipper lies in the fact that it, as noted above, normally is dropped down a manhole which is normally an area of disturbed flow. The liquid flows out of a conduit into the manhole base, which is not coincident with the internal surface of the conduit and thus disturbances are generated effectively changing the depth at that point from what is actually is in the pipe where properties are known. Further, the Manning dipper, when used in a sewer, which transports raw sewage often becomes contaminated and the measurement is thus distorted by the interaction or hang-up of the various particles and material carried by the fluid within the sewer. These interference items cause the approximate pipe depth reading to be even less accurate.
With the above noted disadvantages of the present flow measuring techniques in mind it is an object of the present invention to provide a portable means whereby the flow within an existing regular open channel conduit may be readily and reasonably accurately determined without great costs and further, with far greater accuracy than heretofore possible.
It is another object of the present invention to provide a method whereby the depth within an open channel may be continuously recorded without requiring full time operator surveillance.
Further it is an object of the present invention to provide a novel apparatus for readily measuring the depth of flow in an open channel thus enabling the rate of flow within the channel to be accurately determined.
It is a further object of the present invention to provide an apparatus which consists of a hollow probe which extends linearly into the channel a sufficient distance to avoid disturbances within the manhole and a means for placing and securing that probe accurately such that the depth of flow may be consistently determined without continual surveillance.
It is yet another object of the present invention to provide an apparatus which includes a recording device, a source of gas under pressure and an elongated hollow probe with an orifice in the outermost end such that the gas forced through the outermost end will bubble through the flowing liquid in the open channel. The resistance to the outward flow of the gas can be recorded and thus determine the depth of liquid over the probe and thereby, by use of the Manning formula, the rate of flow of the liquid within the channel.
It is still another object of the present invention to provide a portable means to determine the rate of flow within an open channel wherein the apparatus for determining said flow is located very near the wall of the channel and therefore at a position of theoretical zero velocity, greatly decreasing the possibility of interference with the flow or interference of the measurement by solid particles within the liquid flow.